Cryptosporidium parvum: intensity of infection and oocyst excretion patterns in healthy volunteers

Data about human Cryptosporidium parvum infection have originated from travelers, community and day care center outbreaks, and persons infected with the human immunodeficiency virus. In addition, experimental infection in 29 antibody-negative, healthy, adult volunteers generated information on the dose-infection response of Co parvum (Iowa strain). In that report, low inocula were sufficient to cause infection in 18 and illness in 7 persons. To further define the duration and intensity of infectionin this population, oocystsheddingpatterns wereinvestigatedin the 18subjects infected with Co parvum. Oocyst quantitation revealed that volunteers with diarrheal illness (n = 7) excreted more oocysts over the course of the infection than did volunteers without diarrhea (n = 11;P <.05).Symptomaticsubjectswere more likelyto shed oocystson consecutive days. Further, a statistical nonsignificantinverse trend (r 2 =.330,P =.136)was seen betweenchallenge dose and total excreted oocysts. This paradox may relate to receptor saturation or a toxic effect on cells, parasites, or both afforded by a high inoculum. Cryptosporidium parvum is a conunon enteric protozoan para-site of humans and other species that infects young farm animals (calves, lambs, goats) and pets (kittens,puppies). It is found world